352 Dr. C. Ricketts—Oscillation of the Earth’s Crust. 
between certain identical beds of coal to be one-third greater at 
Standish, near Wigan, than at Prescot, an interval of 13 miles.! 
A most remarkable example of increase in the sedimentary strata 
occurs in the “ Thick” or “Ten Yard” coal of Dudley, which in the 
southern portion is thirty feet thick, having only two to four feet 
of partings ;—that is, during the whole period of its formation it 
remained constantly or nearly at the same level, being that of the 
great Carboniferous plain or delta. Professor Jukes proved that 
this thick bed of coal at a distance of five miles from Bilston in 
a northerly direction, in the neighbourhood of Bentley, is divided 
into ten or twelve separate beds, whose gross thickness is the same, 
but including the intermediate measures has increased to not less 
than 406 feet.’ 
DIAGRAM OF THE DIVISIONS NEAR BENTLEY OF THE **THIcK CoAL’’ OF 
DupLEY AND BILsTon. 
a. Thick Coal at Bilston, 30 feet. 
5. Divisions of same at Bentley, 406 feet. 
e. Heathen Coal. 
Length of Section 5 miles. Altered from Prof. Jukes. 
Conclusion.—F rom all these facts it may safely be inferred, where- 
ever there has been a great accumulation, there also has supervened 
a great amount of depression. Such is the record of the present 
and every geological era. There must needs be a cause for the 
simultaneous occurrence of these phenomena being thus universal, 
inseparable, and in about the same relative proportion. As depres- 
sion could only permit and by no possibility cause accumulation, 
the only reasonable explanation is that accumulation over consider- 
able areas is, through the pressure exerted by its weight, the true 
cause of subsidence. This presupposes a comparatively thin crust 
to the earth resting upon a fluid or semifluid substratum. 
If subsidence occurs in one place, there must, to maintain the 
equilibrium, be elevation in another. Some examples might be 
adduced, both in former geological periods and also at present, where 
elevation has ensued without any reasonable evidence that there has 
been a local withdrawal of pressure. Elevation would more cer- 
tainly supervene upon the removal of pressure, and probably occur 
to a greater extent in the locality whence the detritus has been 
removed the transfer of which has caused subsidence. 
teference has already been made to the results subsequent to the 
1 Geological Survey, Vertical Sections, No. 61. 
* Memoirs of the Geological Survey, The South Staffordshire Coal-field, by J. 
Beete Jukes, F.R.S., p. 25, ete. 
